The “Auto” Range Feature: Best Friend or Worst Enemy?

One of the most widely used features added to cameras in recent years is the “auto” button or “auto range” setting. In “auto mode,” or with the touch of the “auto button,” your imager will automatically adjust the level and span setting to account for the warmest and coolest items in the field of view at that time. Some cameras have a button that is a one-time adjustment, and others have a setting that continuously re-adjusts as the camera pans around and items in the field of view change.

It is a very useful feature for sure, particularly when your inspection location changes from one ambient extreme to another. Remember, the auto feature adjusts the level and span settings to account for the warmest and coolest objects (and everything in between) in the field of view of the camera at that time. If there are extreme temperature variances in the field of view when auto is selected, and at the same time somewhere between those extremes is a thermal anomaly, the auto feature may very well mask it. See Figures One and Two below.

Figure Two

Figure One

These two images are actually the same. In Figure One, the “auto” range was selected. As you can see, the contrast in Figure One is much wider due to the temperature of the thermal foreground of the field of view, which is the very cold morning sky. The warmest surface in each image is clearly the two noted anomalies. Had the thermographer relied solely on the auto feature when taking the above image, the switch anomalies may very well have been missed.

The auto range function must be used with care. In the back of your mind, need to have the thought that the image you see may not be at the optimum level and span settings to detect every possible problem. Manual optimization is still often quite necessary in order to detect lower grade anomalies.

Awareness of the limitations of this feature is the key to success in its use. Use it with care, and it can be your best friend. Use it frivolously and it could turn into your worst enemy.